10,673 research outputs found
The formation of disks in massive spiral galaxies
The flatness of the rotation curve inside spiral galaxies is interpreted as
the imprint of a halo of invisible matter. Using the deepest observations of
distant galaxies, we have investigated how large disks could have been formed.
Observations include spatially resolved kinematics, detailed morphologies and
photometry from UV to mid-IR. Six Giga-years ago, half of the present-day
spirals had anomalous kinematics and morphologies that considerably affect the
scatter of the Tully Fisher relation. All anomalous galaxies can be modelled
through gas-rich, major mergers that lead to a rebuilt of a new disk. The
spiral-rebuilding scenario is proposed as a new channel to form large disks in
present-day spirals and it accounts for all the observed evolutions since the
last 6 Giga-years. A large fraction of the star formation is linked to merging
events during their whole durations.Comment: AIP Proceedings of a review given at the "Invisible Universe
International Conference" held in Paris, June 2009. 16 pages, 9 Figure
Organs from animals for man
In the following review some of the problems of xenotransplantation shall be discussed, based on the few experimental data available so far and on reports in the literature describing investigations which may be of importance for xenotransplantation. The impact of gravity on the upright posture of man versus almost all other mammals, the dysfunction between enzymes and hormones in different species and the lack of interactions between interleukins, cytokines and vasoactive substances will be taken into consideration. The question must be asked whether different levels of carrier molecules or serum proteins play a role in the physiological network. Even though the development of transgenic animals or other imaginative manipulations may lead to the acceptance of any type of xenografted organ, it has to be established for how long the products of the xenografts are able to act in the multifactorial orchestra. We are far from understanding xenogeneic molecular mechanisms involved in toxicity, necrosis and apoptosis or even reperfusion injury and ischemia in addition to the immediate mechanisms of the hyperacute xenogeneic rejection. Here, cell adhesion, blood clotting and vasomotion collide and bring micro-and macrocirculation to a standstill. All types of xenogeneic immunological mechanisms studied so far were found to have a more serious impact than those seen in allogeneic transplantation. In addition we are now only beginning to understand that so-called immunological parameters in allogeneic mechanisms act also in a true physiological manner in the xenogeneic situation. These molecular mechanisms occur behind the curtain of hyperacute, accelerated, acute or chronic xenograft rejection of which only some folds have been lifted to allow glimpses of part of the total scene. Other obstacles are likely to arise when long-term survival is achieved. These obstacles include retroviral infections, transfer of prions and severe side effects of the massive immunosuppression which will be needed. Moral, ethical and religious concerns are under debate and the species-specific production of proteins of the foreign donor species developed for clinical use suddenly appears to be a greater problem than anticipated
The Evolution of the Baryonic Tully-Fisher Relation over the past 6 Gyr
Scaling relations are salient ingredients of galaxy evolution and formation
models. I summarize results from the IMAGES survey, which combines
spatially-resolved kinematics from FLAMES/GIRAFFE with imaging from HST/ACS and
other facilities. Specifically, I will focus on the evolution of the stellar
mass and baryonic Tully-Fisher Relations (TFR) from z=0.6 down to z=0. We found
a significant evolution in zero point and scatter of the stellar mass TFR
compared to the local Universe. Combined with gas fractions derived by
inverting the Schmidt-Kennicutt relation, we derived for the first time a
baryonic TFR at high redshift. Conversely to the stellar mass TFR, the baryonic
relation does not appear to evolve in zero point, which suggests that most of
the reservoir of gas converted into stars over the past 6 Gyr was already
gravitationally bound to galaxies at z=0.6.Comment: To be published in the proceedings of the IAU Symposium 277 "Tracing
the Ancestry of Galaxies"; 4 pages, 1 figur
How was the Hubble sequence 6 Gyrs ago?
The way galaxies assemble their mass to form the well-defined Hubble sequence
is amongst the most debated topic in modern cosmology. One difficulty is to
link distant galaxies to those at present epoch. We aim at establishing how
were the galaxies of the Hubble sequence, 6 Gyrs ago. We intend to derive a
past Hubble sequence that can be causally linked to the present-day one. We
selected samples of nearby galaxies from the SDSS and of distant galaxies from
the GOODS survey. We verified that each sample is representative of galaxies.
We further showed that the observational conditions necessary to retrieve their
morphological classification are similar in an unbiased way. Morphological
analysis has been done in an identical way for all galaxies in the two samples.
We found an absence of number evolution for elliptical and lenticular galaxies,
which strikingly contrasts with the strong evolution of spiral and peculiar
galaxies. Spiral galaxies were 2.3 times less abundant in the past, that is
exactly compensated by the strong decrease by a factor 5 of peculiar galaxies.
It strongly suggests that more than half of the present-day spirals had
peculiar morphologies, 6 Gyrs ago, and this has to be accounted by any scenario
of galactic disk evolution and formation. The past Hubble sequence can be used
to test these scenarios as well as to test evolution of fundamental planes for
spirals and bulges.Comment: Version accepted by Astronomy and Astrophysics, October 21 2009.
Including low resolution images. 11 pages, 8 figure
Galaxy disks do not need to survive in the L-CDM paradigm: the galaxy merger rate out to z~1.5 from morpho-kinematic data
About two-thirds of present-day, large galaxies are spirals such as the Milky
Way or Andromeda, but the way their thin rotating disks formed remains
uncertain. Observations have revealed that half of their progenitors, six
billion years ago, had peculiar morphologies and/or kinematics, which exclude
them from the Hubble sequence. Major mergers, i.e., fusions between galaxies of
similar mass, are found to be the likeliest driver for such strong
peculiarities. However, thin disks are fragile and easily destroyed by such
violent collisions, which creates a critical tension between the observed
fraction of thin disks and their survival within the L-CDM paradigm. Here we
show that the observed high occurrence of mergers amongst their progenitors is
only apparent and is resolved when using morpho-kinematic observations which
are sensitive to all the phases of the merging process. This provides an
original way of narrowing down observational estimates of the galaxy merger
rate and leads to a perfect match with predictions by state-of-the-art L-CDM
semi-empirical models with no particular fine-tuning needed. These results
imply that half of local thin disks do not survive but are actually rebuilt
after a gas-rich major merger occurring in the past nine billion years, i.e.,
two-thirds of the lifetime of the Universe. This emphasizes the need to study
how thin disks can form in halos with a more active merger history than
previously considered, and to investigate what is the origin of the gas
reservoir from which local disks would reform.Comment: 19 pages, 7 figures, 2 tables. Accepted in ApJ. V2 to match proof
corrections and added reference
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